The present invention relates to ink jet printers and the like, and is particularly directed to a method and apparatus for compensation of nozzle plate skew with respect to the perpendicular direction of carrier travel.
Ink jet printers have become extremely popular because of their relatively low cost and high output quality, which can rival that of a laser printer. Ink jet printers use a replaceable cartridge that contains a supply of ink, and a printhead through which the ink is emitted. The cartridge is attached to a carrier which reciprocates along a guide rod in a direction transverse to the direction of travel of the substrate. As the printhead passes over the substrate, such as a sheet of paper, ink drops are emitted through a nozzle plate onto the paper. The ink drops emitted on a single pass of the printhead are referred to as a xe2x80x9cswathxe2x80x9d. While ink jet printers are superior to laser printers in some respects, ink jet printers are typically slower printing devices than laser printers. One method used to enhance printing speed is to increase the size of the nozzle plate in order to reduce printhead traversals of the paper. Unfortunately, an increase in nozzle plate size increases the potential for visually perceptible xe2x80x9cstitchingxe2x80x9d errors. Stitching manifests itself in printed output as skewed vertical lines, blurry text, or through banding and hue shifts. Stitching occurs because of misalignment, or skew, of the nozzle plate with respect to the perpendicular direction of carrier travel, due to, for example, the common stack-up of mechanical tolerances in the various components of an ink jet printer, misalignment of the carrier guide rod with respect to the direction of paper travel, mechanical tolerances of the print nozzle itself, and the inherent difficulty of maintaining a precise alignment of a replaceable cartridge with respect to the carrier. Although stitching is not uncommon, stitching is frequently small enough that it is not perceptible to the human eye when relatively small nozzle plates are used however, as the size of the nozzle plate increases the amount of skew, or stitching, can become great enough to be perceptible to the human eye, especially at the inter-swath boundary.
Given the extremely fine adjustments which would be necessary, mechanical realignment of the nozzle plate with respect to the perpendicular direction of carrier travel by the consumer is impractical. Moreover, because the ink jet cartridge is replaced when the ink supply is exhausted, the amount of stitching can vary from printhead to printhead. Currently, consumers either accept the slight degradation in output caused by such skew, or return the printer to the manufacturer. Neither option is desirable from either the standpoint of the consumer or the manufacturer. Accordingly, it would be beneficial if such skew could be reduced, or eliminated, without requiring mechanical adjustment of the printer. It would also be desirable if such adjustment could be easily made each time a new printhead is installed in the printer.
It is one object of the present invention to provide a method and system for compensating for skew of a printhead nozzle plate with respect to a perpendicular direction of carrier travel without the need for mechanical adjustment of the printer.
It is another object of the present invention to provide a method and system for reducing swath skew with respect to an ideal swath location on a substrate through manipulation of the swath data.
It is still another object of the present invention to provide a method and system for reducing swath skew with respect to a perpendicular direction of carrier travel through modifying a default fire order sequence of a fire group on a nozzle plate.
Additional objects, advantages, and other novel features of the invention will be set forth in part in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the invention. To achieve the foregoing and other objects and in accordance with the purposes of the present invention as described above, a method and system is provided for compensating for skew of a nozzle plate with respect to a perpendicular direction of carrier travel. The method includes receiving feedback regarding swath skew of ink drops generated by a printhead having at least one fire group, the fire group containing a plurality of nozzles. The amount of swath skew can be determined through interaction with a user of the printer, or through skew information generated during post-manufacture testing of printer components. A stream of swath data operative to direct the placement of ink drops by the printhead on a substrate is generated. If the amount of swath skew is greater than a predetermined value, the swath data is modified to create a gross skew adjustment, and a fire order sequence of the plurality of nozzles can be modified to create a fine skew adjustment.
The method and system according to this invention preferably work in a two phase process. Typically, the first phase is initiated upon installation of a new printhead cartridge in the printer, and the amount of swath skew with respect to an ideal swath location on the substrate is determined. A combination of gross skew adjustment, involving shifting of the swath data associated with certain nozzles, and fine skew adjustment, involving modifying a default fire order sequence of the nozzles in certain fire groups, is determined. The gross skew adjustments are applied on a nozzle-by-nozzle basis, and are stored in a persistent memory. The fire order sequence of fire groups is also stored in a persistent memory.
In the second phase, as swath data associated with a print request is generated, the gross skew adjustments are read from memory and applied to the swath data on a nozzle-by-nozzle basis. A controller on the printhead, based on the fine skew adjustments stored in the persistent memory, fires each fire group in its proper fire order sequence.
The gross skew adjustment causes shifts in ink drop placement a distance of one or more pels by modifying, or shifting, the actual swath data. Such an adjustment places individual ink drops within a pel distance from their ideal location. The fine skew adjustment shifts ink drop placement a distance of a fraction of a pel by prematurely initiating or delaying the firing of the nozzles by altering the default fire order sequence of the respective fire group. The application of gross and fine skew adjustments reduces the swath skew to an amount imperceptible to the human eye.
Still other objects of the present invention will become apparent to those skilled in this art from the following description, wherein there is shown and described preferred embodiments of this invention. As will be realized, the invention is capable of other different obvious aspects all without departing from the invention. Accordingly, the drawings and description will be regarded as illustrative in nature and not as restrictive.